Epoxy resin powder coating compositions are utilized in a wide variety of functional and decorative applications which include, for example, corrosion resistant coatings for underground pipe, and steel reinforcing bars, electrical insulating coatings, appliance coatings, and finishes for automotive parts. These powder coatings offer good adhesion, hardness and impact resistance as well as protection from a wide variety of chemical and corrosive environments. In particular, epoxy powder coatings are used extensively for coating pipe used to convey oil and gas. This usage can involve exposure to elevated temperatures and wet conditions. However, conventional epoxy coatings can show significant loss of adhesion when utilized under such hot, wet conditions.
U.S. Pat. No. 4,330,644 discloses a curable composition comprising (1) a solid epoxy composition prepared by reacting (a) a solid epoxy resin prepared by reacting a normally liquid epoxy resin with a polyhydric phenol in the presence of an etherification catalyst with (b) a small amount of tris(hyroxymethyl)aminomethane and (2) at least one epoxy curing agent. The resulting tris-aminomethane modified solid epoxy fusion resin may be cured with conventional epoxy curing agents.
U.S. Pat. No. 4,678,712 discloses a curable coating composition prepared from (1) a component having more than one epoxide group (an epoxy resin) and (2) a component having more than one group reactive with the epoxy groups of components (1) (i.e., a polyhydric phenol). Either component (1) or (2) is the reaction product of a compound containing at least one primary or secondary amino group and at least one aliphatic hydroxyl group (i.e. monoamines having one or two alkanol substituted groups) and with an epoxy resin and optionally a component reactive therewith where the reaction product contains terminal aliphatic hydroxyl groups and epoxy groups or groups reactive with epoxy groups. The components (1) and (2) are preferably normally solid materials and the coating composition is a powder coating composition.
In light of the above, there is a need in the art for epoxy resin systems having a improved hot wet adhesion for coating pipe especially for pipe used to convey oil and gas.